#include <stdio.h>
#include <stdlib.h>

extern char **environ;

int main(void){
    if (setenv("MY_NEW_VAR","new_value",1) != 0){
        /* Handle error */
    }
    if (environ != NULL){
        for (size_t i = 0;environ[i] != NULL; ++i){
            puts(environ[i]);
        }
    }
    return 0;
}